Effect on QTc interval by switching from methadone to equipotent R-methadone dose in methadone maintenance treatment patients

Methadone (R,S-methadone) can prolong the QT interval. R-methadone inhibits cardiac potassium channel function less than S-methadone. We tested if switching from methadone to R-methadone would reduce corrected QT (QTc) intervals in methadone maintenance treatment (MMT) patients. Nine patients, with automatically read QTc intervals ≥450 ms, were required to detect a 20 ms (clinically relevant) reduction in QTc intervals with 15 ms standard deviation (SD) and 90% power. Nine stabilized MMT patients, using median (range) 70 (40-120) mg methadone, were included. Data (ECG recordings, serum samples, and withdrawal symptoms) were collected both before drug intake (Cmin ) and at 3 h after drug intake (Cmax ), and were collected on the day before the switch from methadone to equipotent R-methadone dose and at 14 and 28 days after the switch. A cardiologist calculated QTc intervals retrospectively. Serum electrolytes and methadone concentrations were measured. Mean QTc intervals at Cmin were 472 ms and 422 ms on methadone (automatically and manually read) and 414 ms on R-methadone (manually read). Mean (SD) change in QTc intervals was -8 (10) ms (p = 0.047) at Cmin but non-significant at Cmax . R-methadone showed a concentration-dependent relationship with QTc intervals. Switching to R-methadone reduced QTc intervals, but far less than the 20 ms considered clinically relevant.

Therapeutic drug monitoring of gabapentin in various indications

OBJECTIVES

Gabapentin has been increasingly used in various indications in recent years. Despite variable pharmacokinetics, therapeutic drug monitoring (TDM) is scarcely described in other indications than epilepsy. The aim of the study was to investigate the use and pharmacokinetic variability of gabapentin in epilepsy and non-epilepsy indications and to further evaluate the use of TDM in patients with restless legs syndrome (RLS).

MATERIALS & METHODS

Population-based data from the Norwegian Prescription Database, retrospective TDM data from the section for Clinical Pharmacology, the National Center for Epilepsy, Norway, and prospective observational data on patients with RLS were used.

RESULTS

The use of gabapentin increased by 30% from 2014 to 2017 (32 181 to 42 675 users). TDM data from 120 patients showed a 22-fold pharmacokinetic variability in concentration/dose ratios, and this ratio was elevated in elderly patients (≥65 years). The majority of elderly used gabapentin for non-epilepsy indications. In patients with RLS, intake in the evening/night only was common due to nocturnal symptoms, in contrast to regular dosing regimens in epilepsy. Thus, drug fasting concentrations do not reflect concentrations at the time of required therapeutic effect. TDM was still found useful in most patients to support dosage increase or evaluate adverse effects.

CONCLUSION

Due to extensive pharmacokinetic variability, TDM can benefit patients using gabapentin. Challenges with applying TDM in new indications such as RLS include different dosage regimens and consequently different interpretation of serum concentrations. Thus, TDM should be requested on clear clinical grounds and the service tailored according to the therapeutic indication.

[Drug safety associated with the change of digitalis drug in Norway]

BACKGROUND In 2011, following a period with delivery problems, the only registered digitoxin drug in Norway was replaced with digoxin. As a result, approximately 21 000 patients had to replace digitoxin with digoxin. There are important pharmacokinetic differences between digitoxin and digoxin (the general term for both drugs is digitalis), which must be taken into account when changing therapy. The aim of this study was to investigate compliance of drug security, during the transition from digitoxin to digoxin in Norway.MATERIAL AND METHOD Enquiries addressed to the Norwegian Poison Information Centre and reports of fatal adverse effects to the Regional Drug Information Centres (RELIS) regarding intake of digitalis were analysed. Serum concentrations of digitoxin and digoxin analyzed at Oslo University Hospital were reviewed. All data sources were reviewed for the years 2010-2014 and patients > 20 years were included.RESULTS The total number of enquiries addressed to the Norwegian Poison Information Centre, fatal adverse drug reactions reported to RELIS, and patient samples in the toxic range analyzed at Oslo University Hospital increased from 2012, timewise related to the transition to digoxin.INTERPRETATION Despite extensive information from the Norwegian Medicines Agency, a small, transient increase was observed in the number of overdoses and reported deaths from digitalis related to change in therapy. The cause of the overdose was in many cases unknown. This study revealed several cases of incorrect dosage, simultaneous use of digitoxin and digoxin, and washout time that was insufficient or lacking before initiation of digoxin.

Effects of Hemodialysis on Methadone Pharmacokinetics and QTc

PURPOSE

Effects of hemodialysis on pharmacokinetic properties and QTc were studied in 4 patients taking daily methadone dose of 100 mg (range, 60-120 mg).

METHODS

Methadone in serum, dialysate, and urine were measured by LC-MS/MS. QTc was calculated with Bazett's formula.

FINDINGS

The serum Cmin methadone level was 1124 nmol/L (range, 547-1581 nmol/L). Methadone dialysate clearance was 17.1 mL/min (range, 13.7-20.6 mL/min). Total loss in dialysate was 2.30% (range, 1,25-3,70%) of daily methadone intake. QTc increased from 391 msec (range, 369-406 msec) to 445 msec (range, 407-479 msec), independently of serum methadone level, which may be explained by normalization of serum electrolytes.

IMPLICATIONS

Methadone dose adjustment is not needed because of hemodialysis.

Determination of digoxin and digitoxin in whole blood

A liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for the determination of digoxin and digitoxin in whole blood samples in autopsy cases. Samples were prepared by liquid-liquid extraction (LLE) with ethyl acetate/heptane/dichloromethane (3:1:1). LC separation was achieved using an Atlantis dC(18)-column (2.1 x 50 mm, 3 microm). The time between injections was 11 min. Mass detection was performed by positive ion mode electrospray LC-MS-MS on the ammonium adducts with two transitions for each analyte and one for the internal standard (digoxin-d(3)). Within-day precision was between 8.3 and 10.8%, between-day precision was between 8.7 and 14.2% and accuracy (bias) was between -17.3 and 11.5%. LOQ was 0.1 nmol/L (0.08 ng/mL), with an accuracy and precision of 19% and -17% (digoxin) and 18% and 3% (digitoxin). Matrix effects ranged from 104 to 117%. Good qualitative correlation with previous findings was achieved for 38 autopsy cases. The median (range, number of cases) B-digitoxin and B-digoxin found with the LC-MS-MS method in this very limited material were 9.3 (3.4-23.8, n = 24) and 5.6 (3.4-26.5, n = 4) nmol/L, respectively.

Blood alcohol concentrations in apprehended drivers of cars and boats suspected to be impaired by the police

OBJECTIVE

According to the Norwegian Road Traffic Act, car drivers are not allowed to operate a vehicle with a blood alcohol concentration (BAC) above 0.2 g/kg. Depending on the size of the boat or ship, boat drivers/captains/first mates are not allowed to conduct the boat with a BAC above 0.8 g/kg when driving small boats (length less than 15 m) and above 1.5 g/kg when running larger vessels/ships. The new Sea Act of June 2005 states that captains/first mates cannot conduct a ship if he/she has a BAC above 0.2 g/kg. Our aim was to determine the current median BAC in a large population of car and boat drivers in Norway. Our other aim was to study if median BAC was higher in boat drivers than in car drivers who were suspected by the police to be impaired. Furthermore, we wanted to investigate if the BAC levels were differently distributed by gender or age within and between these two groups.

METHODS

The Norwegian Institute of Public Health analyzes blood samples from all car/boat drivers suspected of driving under the influence of alcohol and non-alcoholic drugs. In the present study, samples submitted between 01.05 and 01.09 in 2002-2004 were included. Drivers, who in addition tested positive for drugs or abuse substances other than ethanol were excluded.

RESULTS

There were 321 boat drivers and 3,061 car drivers who were suspected to be under the influence of ethanol only. The median BAC in boat drivers (1.76 g/kg [range 0.02-3.54]) was significantly higher compared to that in car drivers (1.54 g/kg [range 0.00-4.27]). In the car driver group, the mean BAC did not differ significantly between men and women. The median level of BAC was significantly higher in men than in women in the boat driver group (1.77 g/kg with CI 1.69-1.85 vs. 1.27 g/kg with CI 0.78-1.76).

CONCLUSIONS

Alcohol impairment of car drivers is known to be considered the most important contributing cause of car crash injuries. Driving a boat may demand the same degree of performance skills as driving a car. The median BAC in apprehended boat drivers was considerably high in the present study. The median BAC was also high in car drivers despite strict legislation. The population of drivers of cars in our study, however, is from previous studies known to contain a large proportion of heavy drinkers. Less is known about the drinking habits in boat drivers, and caution is needed in generalizing from our results. However, our results indicate the possible need for stricter legislation and more frequent police control that will hopefully prevent serious accidents caused by ethanol drinking at sea.

Relationship between methadone and EDDP (2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine) in urine samples from Norwegian prisons

BACKGROUND

Methadone maintenance treatment is a widely used therapy in the rehabilitation of opioid addiction the world over. Methadone is metabolised in the body to a number of inactive metabolites, but primarily to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). The Division of Forensic Toxicology and Drug Abuse (DFTDA) of the Norwegian Institute of Public Health carries out drug analysis of urine samples from inmates of prisons throughout Norway. Methadone and EDDP in the urine are also tested for upon request. The results are stored in a secure database at the DFTDA.

OBJECTIVES

The aims of the present study were (1) to observe variations in methadone and EDDP concentrations in urine in relation to urine pH in a large set of urine samples obtained from prison inmates and (2) to analyse samples testing methadone-positive/EDDP-negative and investigate whether such results could occur naturally, without sample tampering.

METHODS

All urine samples that tested positive for methadone over the period 2004-2005 were collected from the DFTDA database, and the relation between methadone and EDDP excretion in urine, and urinary pH was determined. Samples that tested positive for methadone but negative for EDDP were picked out and studied individually.

RESULTS

A total of 1539 urine samples (cases) had tested positive for methadone in our database for the period 2004-2005. There was a strong correlation between the concentration of methadone in urine and urine pH in these samples, with higher concentrations of methadone present at lower pH levels. Cases that tested positive for methadone but negative for EDDP were rare - a total of five (0.3% of all cases tested). These cases were studied in more detail.

CONCLUSION

Methadone excretion in urine is dependent on urinary pH. Methadone-positive/EDDP-negative results may suggest sample tampering in some, but not all, cases.

Simultaneous determination of 6 beta-blockers, 3 calcium-channel antagonists, 4 angiotensin-II antagonists and 1 antiarrhytmic drug in post-mortem whole blood by automated solid phase extraction and liquid chromatography mass spectrometry

A method for the simultaneous determination of the beta-blockers atenolol, sotalol, metoprolol, bisoprolol, propranolol and carvedilol, the calcium-channel antagonists diltiazem, amlodipine and verapamil, the angiotensin-II antagonists losartan, irbesartan, valsartan and telmisartan, and the antiarrhythmic drug flecainide, in whole blood samples from forensic autopsies was developed. Sample clean-up was achieved by precipitation and solid phase extraction (SPE) with a mixed-mode column. Quantification was performed by reversed phase high performance liquid chromatography with positive electrospray ionization mass spectrometric detection (HPLC-MS). The method has been developed and robustness tested by systematically searching for satisfactory conditions using experimental designs including factorial and response surface designs. With the exception of amlodipine, the concentration limit of quantification (cLOQ) covered low therapeutic concentration levels for all the compounds. Within assay precisions and accuracies (bias) were 3.4-21% RSD and from -24 to 21% for the concentration range 1.00-5.00 microM, respectively. Between assay precisions were 4.4-28% RSD for the concentration range from 0.1 to 5 microM and recoveries varied from 9 to 103%. The method is used for determination of cardiovascular drugs in post-mortem whole blood samples from forensic autopsy cases.

[Khat--a new drug of abuse in Norway]

BACKGROUND

The stimulating drug, Khat, is a drug of abuse that has become known in Norway due to increased immigration from East-Africa, especially Somalia.

METHOD

Review of recent literature.

RESULTS

Khat is present in leaves from the tree Catha Edulis and is taken by chewing the leaves. The biologically active compounds are cathinone, cathine and norephedrine. Analysis of cathinone in urine can be performed at the Norwegian Institute of Public Health. The effects of khat are similar to, but weaker than those of amphetamine. Khat stimulates the central nervous system causing increased alertness, euphoria and occasionally psychosis, and increases activity in the peripheral sympathetic nervous system leading to palpitations, increased blood pressure, large pupils and red eyes. Tannin in khat damages teeth and causes constipation. With increased use of khat in the society it is important for the clinician to have some knowledge of the effects of khat.